The term “adjustable element” should in this case be understood in the all-encompassing sense. Correspondingly, this term includes any adjustable elements in a motor vehicle, such as a tailgate, a deck lid, an engine bay cover, a cargo compartment cover, a side door—including a sliding door—, a cargo floor and a sunroof of a motor vehicle. In addition, these include, for example, motor-adjustable window panes, mirrors or vehicle seats.
With the aim of increasing comfort in modern motor vehicles, the motor-driven adjustment of the abovementioned adjustable elements, for example the tailgate, of a motor vehicle is gaining increasing importance. For this purpose, a drive arrangement is provided which is coupled to the respective adjustable element via a drive train.
The known drive arrangement (EP 1 862 628 A1), on which the present invention is based, is equipped with two electrical drives. The two drives are configured in the form of spindle drives and each have an electrical drive motor with a spindle/spindle nut transmission connected downstream thereof. The two spindle drives are arranged on the two peripheral sides of a tailgate and each act independently, but in the same way, on the tailgate. The two spindle drives are arranged correspondingly such that, given the same drive forces, they introduce the same drive torques on both peripheral sides into the tailgate.
For the motor-driven adjustment of the tailgate, generally the same drive voltage is applied to the two spindle drives. In this case, it is assumed that the motor characteristics of the two drive motors are identical.
However, it has been shown in trials that the motor characteristics of the drive motors in question are subject to tolerance-related differences. This results, inter alia, in different drive currents and correspondingly different drive forces or torques being established for identical drive speed and identical drive voltage. That is to say that one drive will always consume more electrical power and output correspondingly more mechanical power than the other drive. This generally results in the drive which is always subject to a greater load having a reduced life.
Various control engineering approaches for driving the drive arrangement in question have been disclosed, for example a control device in which specifically determined open-loop and/or closed-loop control concepts are used for each adjustment phase of the adjustable element (EP 1 860 265 A2). However, the aspect of non-uniform wear on the two drives is not addressed in this document either.